U.S. patent number 6,771,086 [Application Number 10/079,329] was granted by the patent office on 2004-08-03 for semiconductor wafer electrical testing with a mobile chiller plate for rapid and precise test temperature control.
This patent grant is currently assigned to Lucas/Signatone Corporation. Invention is credited to Lloyd B. Dickson, Ralph James Eddington, Robert C. Lutz.
United States Patent |
6,771,086 |
Lutz , et al. |
August 3, 2004 |
Semiconductor wafer electrical testing with a mobile chiller plate
for rapid and precise test temperature control
Abstract
A semiconductor-wafer chuck for heating and cooling a
device-under-test includes a heat-spreader plate with a clamping
surface for a semiconductor wafer. A heater is disposed within the
heat-spreader plate. A chiller heat-exchanger provides for heat
removal. A motion control system is used to move the chiller
heat-exchanger in relation to the heat-spreader plate, and thus
provide for an adjustment of the thermal resistance and thermal
coupling between the two. The heater comprises electric heating
elements with a variable power input, and the chiller
heat-exchanger is moved sufficiently far away to prevent boiling
and evaporation of a coolant disposed inside. A device-under-test
temperature controller controls the device-under-test temperature
by adjusting the heater power, chiller fluid temperature and/or by
moving the chiller heat-exchanger in relation to the heat spreader
plate.
Inventors: |
Lutz; Robert C. (Sunnyvale,
CA), Dickson; Lloyd B. (Sunnyvale, CA), Eddington; Ralph
James (Newman, CA) |
Assignee: |
Lucas/Signatone Corporation
(Gilroy, CA)
|
Family
ID: |
27733016 |
Appl.
No.: |
10/079,329 |
Filed: |
February 19, 2002 |
Current U.S.
Class: |
324/750.09;
165/80.2; 324/762.05 |
Current CPC
Class: |
G01R
31/2865 (20130101); G01R 31/2874 (20130101); G01R
31/2891 (20130101); G01R 31/2887 (20130101) |
Current International
Class: |
G01R
31/28 (20060101); G01R 031/02 (); F28F
007/00 () |
Field of
Search: |
;324/754,760,765
;118/712 ;432/81,120-122,137,152,197 ;266/87-88 ;165/80.2-80.5 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4609037 |
September 1986 |
Wheeler et al. |
4784213 |
November 1988 |
Eager et al. |
5885353 |
March 1999 |
Strodtbeck et al. |
6073681 |
June 2000 |
Getchel et al. |
6313649 |
November 2001 |
Harwood et al. |
6394797 |
May 2002 |
Sugaya et al. |
6471913 |
October 2002 |
Weaver et al. |
|
Primary Examiner: Karlsen; Ernest
Assistant Examiner: Kobert; Russell M.
Attorney, Agent or Firm: Law Offices of Thomas E.
Schatzel
Claims
What is claimed is:
1. A semiconductor-wafer tester, comprising: a heat-spreader plate
providing a clamping surface for a semiconductor wafer; a heater
disposed within the heat-spreader plate and providing for
temperature elevations; a chiller heat-exchanger mobile and
independent of the heat-spreader plate and providing for heat
removal; a continuously variable-width gap separating the chiller
heat-exchanger in relation to the heat-spreader plate providing for
continuous thermal resistance and coupling adjustments of heat
sinking out of said semiconductor wafer; and a position control
system connected to adjust the continuously variable-width gap.
2. The semiconductor-wafer tester of claim 1, wherein: the heater
comprises electric heating elements that can be power controlled
including full on or off; and the chiller heat-exchanger is moved
sufficiently far enough away to prevent boiling and evaporation of
a coolant disposed inside when the heater is under power.
3. The semiconductor-wafer tester of claim 1, further comprising: a
device-under-test-temperature controller with electrical outputs
connected to the heater and connected to the position control
system, and having an input for sensing the temperature of a
device-under-test clamped to the heat-spreader plate, and further
providing for the control of said temperature by controlling the
heater power and by moving the chiller heat-exchanger in relation
to the heat-spreader plate.
4. The semiconductor-wafer tester of claim 3, further comprising: a
limiter disposed in the device-under-test-temperature controller
for limiting the movement of the chiller heat-exchanger in relation
to the heat-spreader plate according to a maximum supportable heat
load.
5. The semiconductor-wafer tester of claim 1, further comprising: a
vacuum for clamping said semiconductor wafer to said clamping
surface; and an external chiller connected to circulate coolant to
the chiller heat-exchanger.
6. A means for heating and cooling a device-under-test, the method
comprising the steps of: means for providing a heat-spreader plate
with a clamping surface for a device-under-test; variable
separation-gap positioning means for continuous adjustment between
a minimum and a maximum of a thermal resistance from said
heat-spreader plate to a chiller heat-exchanger; means for heating
said heat-spreader plate by incrementally increasing said thermal
resistance from it to a chiller heat-exchanger; and means for
cooling said heat-spreader plate by incrementally decreasing said
thermal resistance from it to said chiller heat-exchanger.
7. The means of claim 6, wherein: the means for heating is such
that an increase in said thermal resistance to said chiller
heat-exchanger is sufficient to prevent boiling of a coolant fluid
circulating within said chiller heat-exchanger.
8. The means of claim 6, wherein: the means for heating is such
that said chiller heat-exchanger is maintained at an idle
temperature.
9. The means of claim 6, wherein: the means for cooling further
includes using a chiller heat-exchanger in which is circulated a
fluid comprising a fluorocarbon.
10. The means of claim 6, further comprising: means for limiting
any heat loading of a chiller circulating a coolant to said chiller
heat-exchanger by controlling a change in said thermal
resistance.
11. The means of claim 6, further comprising: means for measuring
the temperature of said heat-spreader plate; and means for
controlling said thermal resistance to maintain a setpoint
temperature according to information obtained in the step of
measuring.
Description
1. FIELD OF THE INVENTION
The present invention relates to methods and devices for cycling
the temperature of a device-under-test, and more particularly to
chuck systems for semiconductor wafers that provide for rapidly
obtained set-point temperatures over a wide control range.
2. DESCRIPTION OF THE PRIOR ART
Thermal testing systems used in the semiconductor industry have
advanced to the point that wide temperature variations for device
testing can be induced in semiconductor wafers. For example,
Temptronic Corporation (Sharon, Mass.) markets a thermal test
system called THERMOCHUCK.RTM.. This thermal inducing vacuum
platform allows for wafer probing, testing, and failure analysis at
precise, controlled temperatures. Wafers as big as 300-mm in
diameter can be accommodated and temperature controlled with a
range of -65.degree. C. to +400.degree. C.
A modern wafer probing system is described by Warren Harwood, et
al., in U.S. Pat. No. 6,313,649 B2, issued Nov. 6, 2001, and titled
WAFER PROBE STATION HAVING ENVIRONMENT CONTROL ENCLOSURE. A
positioning mechanism is included to facilitate microscopic
probing.
Operating temperatures over +200.degree. C. and certainly those as
high as +400.degree. C. resulted in a prior art requirement to
valve cooling air and liquid coolant between high temperature and
low temperature evaporators. One such arrangement is described by
George Eager, et al., in U.S. Pat. No. 4,784,213, issued Nov. 15,
1988, and titled MIXING VALVE AIR SOURCE.
Typical device-under-test chucks used for probing semiconductor
wafers have a flat plate with holes in it so the semiconductor
wafer can be drawn tightly down with a vacuum. For example, see
U.S. Pat. No. 6,073,681, issued to Paul A. Getchel, et al., on Jun.
13, 2000, for a WORKPIECE CHUCK. The flat plate usually has an
electric heater and a chiller heat-exchanger for heating and
cooling the device-under-test. A fluorocarbon liquid is pumped from
an external chiller through the chiller heat-exchanger to bring the
temperature down below -65.degree. C. The electric heating elements
can raise the device-under-test temperature as high as +400.degree.
C. Thermocouples are used to measure the chuck temperature and
provide feedback to a closed-loop control system with a temperature
setpoint manipulated by a user.
William Wheeler describes a hot/cold chuck in U.S. Pat. No.
4,609,037, issued Sep. 2, 1986. An electric heater is used in a top
plate and a coolant circulating plate below it is brought in
contact during the cooling phase. A power and control system for
such a device-under-test chuck is described in U.S. Pat. No.
6,091,060, issued Jul. 18, 2000, to Getchel, et al.
Unfortunately, the fluorocarbon liquid pumped from the external
chiller through the chiller heat-exchanger is subject to boiling
and evaporation loss when the electric heaters are used. Such
fluorocarbon liquids are very expensive, and even a teaspoonful
loss every temperature cycle can add up to thousands of dollars of
expense over a relatively short time.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
method for rapidly heating and cooling a device-under-test.
It is another object of the present invention to provide a vacuum
chuck system that is simple and inexpensive to manufacture and
operate.
Briefly, a semiconductor-wafer chuck embodiment of the present
invention provides for heating and cooling of a device-under-test.
It includes a heat-spreader plate with a clamping surface for a
semiconductor wafer. A heater is disposed within the heat-spreader
plate and provides for temperature elevations. A chiller
heat-exchanger independent of the heat-spreader plate provides for
heat removal. A position control system is used to move the chiller
heat-exchanger in relation to the heat-spreader plate, and thus
provide for an adjustment of the thermal resistance and thermal
coupling between the two. The heater typically comprises electric
heating elements with a controlled power input including full on
and off, and the chiller heat-exchanger is moved sufficiently far
enough away to prevent boiling and evaporation of a coolant
disposed inside when the heater is switched on. A
device-under-test-temperature controller has outputs connected to
the heater and the position control system, and an input for
sensing the temperature of a device-under-test clamped to the
heat-spreader plate. It then can control the device-under-test
temperature by controlling the heater power, and/or by moving the
chiller heat-exchanger in relation to the heat-spreader plate.
An advantage of the present invention is that a method is provided
for rapid heating and cooling of devices-under-test.
Another advantage of the present invention is that a hot/cold
vacuum chuck system is provided that does not boil off and
evaporate coolant, and therefore is inexpensive to operate.
A further advantage of the present invention is that a hot/cold
chuck system is provided that avoids the use of complex valving
systems for coolant circulation and control, and therefore is less
expensive to manufacture.
Another advantage of the present invention is that a hot/cold chuck
system is provided that does not depend on valves to route coolant
and cool-down air.
A still further advantage of the present invention is that a
hot/cold chuck system is provided that does not need to expel
vapor, fumes or gases too hot for plastic pipes and pieces to be
used.
These and other objects and advantages of the present invention
will no doubt become obvious to those of ordinary skill in the art
after having read the following detailed description of the
preferred embodiments which are illustrated in the various drawing
figures.
IN THE DRAWINGS
FIG. 1 is a schematic diagram of a device-under-test
heating-and-cooling embodiment of the present invention;
FIG. 2 is a block diagram of a wafer-probing system embodiment of
the present invention and includes a hot/cold chuck based on the
elements of FIG. 1;
FIGS. 3A and 3B are cross-sectional diagrams of a hot/cold vacuum
chuck embodiment of the present invention like that shown in FIG.
2, FIG. 3A shows the cooling heat-exchanger close to the top of its
travel, and FIG. 3B shows it close to its bottom travel limit;
FIG. 4 is a perspective view diagram of a hot/cold vacuum chuck
embodiment of the present invention like that shown in FIG. 2
mounted on an X-Y-Z positioning platform to facilitate
semiconductor wafer probing;
FIG. 5 is a cross-sectional close-up diagram of a hot/cold vacuum
chuck embodiment of the present invention like that shown in FIG.
2, and showing some details of the quartz ring supports;
FIG. 6 is a chart showing a cool-down test of a hot/cold vacuum
chuck embodiment of the present invention like that shown in FIG.
2; and
FIG. 7 is a chart showing a heat-up test of a hot/cold vacuum chuck
embodiment of the present invention like that shown in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates a device-under-test chuck heating-and-cooling
method embodiment of the present invention, and is referred to
herein by the general reference numeral 100. Embodiments other than
this one are more preferred in many applications. However, this
embodiment provides a good vehicle here to discuss the principle
critical components and methods used in all embodiments.
The method 100 provides a heat-spreader plate 102 with a clamping
surface 104 for a device-under-test 106. The device-under-test 106
is typically a semiconductor wafer device-under-test that is heated
and cooled to various setpoint temperatures for probing and failure
analysis. The method 100 includes allowing the rapid heating of the
heat-spreader plate 102 by increasing a variable thermal
resistance, represented by schematic symbol 108, to a chiller
heat-exchanger 110. The heat-spreader plate 102, and therefore the
device-under-test 106, are cooled by decreasing the thermal
resistance 108 and thus increasing the thermal coupling to the
chiller heat-exchanger 110.
The thermal resistance 108 is not a physical part, it represents
the effect of moving the chiller heat-exchanger 110 relative to the
heat-spreader plate 102.
The heat-spreader plate 102 unavoidably has a thermal mass that can
slow down temperature ramping. However, in order to spread heat
well, it must be constructed of metal and metal will have a
significant thermal mass. What is important is the ratio of the
thermal masses of the heat spreader and the chiller heat-exchanger.
When the chiller heat-exchanger has a large thermal mass relative
to the spreader, the temperature increase it experiences when
brought into to contact with a hotter spreader plate is reduced,
easing fluid overheating problems.
One way to increase the thermal resistance 108 is accomplished by
increasing a separation distance between the heat-spreader plate
102 and the chiller heat-exchanger 110. This would lengthen the
path heat would have to travel over the thermally inefficient air
gap. Alternatively, the step of heating comprises increasing the
thermal resistance by introducing a lesser thermally conductive
intervening medium between the heat-spreader plate and the chiller
heat-exchanger, e.g., a vacuum.
The step of cooling comprises decreasing the thermal resistance by
decreasing a separation distance between the heat-spreader plate
102 and the chiller heat-exchanger 110. Alternatively, the step of
cooling comprises decreasing the thermal resistance by introducing
a more thermally conductive intervening medium between the
heat-spreader plate and the chiller heat-exchanger, e.g., a dense
gas or liquid.
A positioning motor 112 with a leadscrew or jackscrew 114 can be
used to position the chiller heat-exchanger 110 closer to or
farther from the heat-spreader plate 102. At the minimum thermal
resistance 108, the heat-spreader plate 102 may be in full face
contact with the chiller heat-exchanger 110. A useful maximum
separation was discovered to be only a scant 0.30 inches. A
positioning controller 116 can be used to control the effective
thermal resistance 108. A setpoint temperature (S) 118 is compared
to a device-under-test temperature (T) 119 and the difference
causes control signals to be developed for an electric heater 120
via heater controller 116 and an external chiller 124. An electric
power source 126 supplies operating current to the heater 120. The
heater is operated after the heat-spreader plate 102 and chiller
heat-exchanger 110 are separated, and then the external chiller 124
is idled. A typical idle temperature for the chiller heat-exchanger
is 0.degree. C., and this helps to heat shield any control
electronics disposed below and inside an environmental chamber 128.
A dry atmosphere 130 is disposed and maintained inside the
environmental chamber 128 to prevent and control frosting.
In general, the thermal resistance 108 to the chiller
heat-exchanger is preferably sufficient to prevent boiling off a
coolant fluid circulating within the chiller heat-exchanger 110
when the heater 120 is operating. The chiller heat-exchanger 110
and external chiller 124 typically circulate a fluid comprising a
fluorocarbon, e.g., as marketed by 3M Company.
The temperature control system 116 is a supervisory controller,
most likely implemented as a program running on a small single
board computer. It may receive instructions from a main probing
system-computing controller or directly from a built-in control
panel. It issues setpoint values to two temperature controllers,
typically via RS-232 interfaces. The controllers control the
chiller fluid temperature and the heat-spreader temperature. The
temperature controllers may be built into the chiller and heater
power supply, as hinted in FIG. 2. The supervisory controller also
controls the heat-exchanger positioning. This may be via a motor
servo loop, open control system, or perhaps by a less complex
control strategy. The movement primarily controls position and does
not necessarily directly control temperature. Heater power is
generally turned off during cooling.
FIG. 2 illustrates a wafer-probing system embodiment of the present
invention, and such is referred to herein by the general reference
numeral 200. The wafer-probing system 200 includes a hot/cold chuck
202 mounted on a motion stage 204 inside an enclosure 206. An air
drier 208 supplies dry air that will not form frost on the
components inside enclosure 206. A probe 210 provides for
semiconductor wafer testing on the chuck 202. A chuck heater power
supply and temperature controller 212 operate on heating cycles,
e.g., to +400.degree. C. A recirculating fluid chiller and
temperature controller 214 chill a movable cooling heat-exchanger
215 during cooling cycles, e.g., to as low as -80.degree. C. An
electronic test instrument 216 may be electrically connected to the
probe 210 and the chuck 219 to measure the electrical parameters of
the DUT (Device Under Test) 221.
In particular, the thermal system supervisory controller 217 can
operate a cooling-heat-exchanger-positioning motor 220 to increase
or decrease the effective thermal coupling between the cooling
heat-exchanger 215 and the fixed top portion of chuck 202. The
probing system computing controller 218 provides direction to and
receives data from the instrumentation 216. The thermal systems
supervisory controller 217 could be integral to the computing
controller 218, but is equally likely to be built into a separate
box with a human interface, or a separate box which receives
control instructions from the computing controller 218.
FIGS. 3A and 3B represent a hot/cold vacuum chuck embodiment of the
present invention like that shown in FIG. 2, and are referred to
herein by the general reference numeral 300. One or more additional
layers 304 may cover the heat spreader plate 302 to enhance
electrical measurement capabilities by reducing noise and leakage
currents. Typically these layers are alternately thin insulator and
conducting sheets, which may variously be fabricated as solid
plates, metallic foils, and/or deposited films.
The hot/cold vacuum chuck 300 primarily heats or cools the
semiconductor wafer 306 to various target temperatures so probing
tests and failure analysis can conducted. FIG. 3A shows how during
cooling of the semiconductor wafer 306 a cooling heat-exchanger 308
is lifted by a set of jackscrews 310 and 312 to be in close
proximity or contact with the heat spreader 302. An electric heater
element 314 is turned off during cooling. A set of motors, or a
motor and belt, can be used to run the jackscrews 310 and 312 up
and down as needed. Alternatively, a manually driven thumbscrew can
be manipulated for the same purpose.
FIG. 3B shows how during heating of the semiconductor wafer 306 the
cooling heat-exchanger 308 is dropped down away from the heat
spreader 302 by the jackscrews 310 and 312. The electric heater
element 314 is turned on during heating. The separation distance
between the heat spreader 302 and the cooling heat-exchanger 308
removes a major part of the heat load from the cooling system.
FIG. 4 is a perspective view diagram of a hot/cold vacuum chuck
embodiment of the present invention like that shown in FIG. 2, and
is referred to herein by the general reference numeral 400. A
semiconductor wafer 402 being tested is placed on the
vacuum-clamping surface 404 of a heat spreader 406. The electrical
heater is built into the heat spreader 406 that has a fixed
position. A moveable cooling plate 408 can be moved up and down by
the motion control motor. A base plate 414 supports the above
components and is pierced by coolant supply and return piping 416.
A positioning stage 418 is mounted on a base foundation 420 and can
adjust the X-Y-Z and angular (.O slashed.) position of the
semiconductor wafer 402 during probing.
FIG. 5 represents a hot/cold vacuum chuck 500 in a preferred
embodiment of the present invention. A sandwich of plates 502 and
504 are clamped to the top of a heat-spreader plate 506. In this
embodiment the lower plate 504 may be an insulator, and the upper
plate 502 may be a conductor.
A cooling heat-exchanger 508 with coolant chambers 510 is raised
and lowered on a jackscrew 512 driven by a positioning motor, e.g.,
via lift mechanism 514. Such motion will adjust the effective
thermal coupling and thermal resistance between the heat-spreader
plate 506 and the cooling heat-exchanger 508. A clamping ring 516,
a spring 518, and a fastener 520 clamp the edge of an annular,
quartz support ring 522 to mount the heat spreader and top plate
assembly to the base 524. The support ring 522 has the shape of a
straight, parallel section of a hollow right cylinder. For example,
it could be cut from a length of large-diameter glass tubing.
The operating range of the hot/cold vacuum chuck 500 can span
-80.degree. C. to +400.degree. C., and so the expansion and
contraction of these pieces can be substantial. The quartz support
ring 522 tolerates such extreme heating and cooling very well, and
provides a solid support from a base plate 524. A protective shield
526 surrounds the quartz support ring 522 all around its circular
perimeter.
The annular, quartz support ring 522 is a critical component in
many embodiments of the present invention. It places a support
member with a crucial low-coefficient of thermal expansion at a
place that principally defines the plane of the top surface of the
work area.
FIG. 6 is a chart 600 showing a cool-down test of a hot/cold vacuum
chuck embodiment of the present invention like that shown in FIG.
2. Three thermocouples were attached to various points on the
chuck: a first on a heat spreader (Ts), a second to the top surface
of the chuck near the edge (Te), and the third to the top surface
of the chuck near the center (Tc). A fourth thermocouple was
attached to a chiller heat-exchanger. These respectively produced
temperature curves 601-604. At time zero, e.g., 0.00 minutes, the
device-under-test was stabilized at over 200.degree. C. and the
cooling heat-exchanger was idling at 0.degree. C. In the first
minute, the heater was turned off, the chiller reactivated, and the
cooling plate moved in to thermally couple with the heat-spreader
and device-under-test. This caused a small bump in curve 604, but
not so high as to evaporate the coolant or cause it to decompose
into potentially non-benign constituents. The curves 601-603 drop
precipitously, and demonstrate good performance. The surface of the
spreader plate was stabilized at less than -60.degree. C. in less
than forty minutes. Faster speeds are possible.
FIG. 7 is a chart 700 showing an actual heat-up test of the
hot/cold vacuum chuck mentioned in connection with FIG. 6. which
starts from an extremely cold temperature. The thermocouples
attached to various points respectively produced temperature curves
701-704. The heater was inadvertently shut off in the 8-9 minute
period. The graph is nevertheless informative.
At time zero, e.g., 0.00 minutes, the device-under-test was
stabilized at under -60.degree. C. and the cooling heat-exchanger
was running at maximum. In the first minute, the heater was turned
on and the chiller set to 0.degree. C., but the cooling plate
remained in contact with the heat spreader. At 7 minutes the
cooling heat-exchanger was positioned far away from the heat
spreader. This allowed the temperatures to rapidly separate, e.g.,
as seen in the diversion of curves 701-703 from curve 704. The
curves 701-703 plateau above +200.degree. C. in under fifteen
minutes.
A preferred system embodiment of the present invention uses two
temperature controllers, and one chiller heat-exchanger positioner.
One temperature controller controls the electric heater plate, and
the other controls the chiller fluid temperature, for example,
controllers 212 and 214, A third controller controls the
positioning motor 220 (FIG. 2). These three controllers and
positioners are, in turn, connected to a master controller, e.g.,
the thermal systems supervisory controller 217 (FIG. 2).
Alternately, such supervisory controller could be realized in
software within the probing system computing controller 218.
Lesser-preferred embodiments of the present invention allow the
heating and cooling systems to battle one another. For instance,
where the heater is left on and the chiller heat-exchanger position
is moved in and out to hold a desired device-under-test
temperature. Typically this method would be inefficient, but may
have other advantages such as faster response time or enhanced
temperature accuracy.
Therefore, a preferred operating-method embodiment of the present
invention begins by heating a device-under-test chuck from near
room temperature. To do this without causing a battle with the
cooling system, the chiller's heat-exchanger is lowered away to
open up a large insulating gap. The chiller-fluid temperature
controller is reset to a moderate temperature setpoint, e.g.,
0-25.degree. C. The electric-heat controller is used to
proportionally control heater-power to maintain the desired hot
temperature setpoint.
The device-under-test is cycled cold by idling electric-heat
controller, i.e., to essentially turn off the heater filaments. The
fluid temperature of the chiller system is brought near to the
desired cold temperature by issuing a setpoint-value to the
chiller-fluid controller. Then the chiller's heat-exchanger is
moved close enough to the heater plate to instigate rapid cooling,
but not close enough to overheat the chiller fluid or induce plate
warping. In less extreme temperature ramping, such chiller fluid
boiling and plate warping will not be an issue. So when it is
"safe", the chiller heat-exchanger can be raised to actually
contact the heater plate. The chiller-fluid controller then
operates to further reduce the device-under-test chuck temperature
to the cold setpoint-value.
The device-under-test chuck temperature is brought up from cold
temperatures by first sending the chiller chiller-fluid controller
a setpoint-value near room temperature, e.g., 0.degree. to
25.degree. C. The desired hot setpoint-value is sent to the
electric-heat controller, and heating commences. The chiller
heat-exchanger contact with the heater plate is preferably
maintained until the chiller fluid temperature comes up to the
desired fluid idle temperature. The chiller heat-exchanger is then
moved away to its maximum separation position. Such frees the
electric-heat controller to more rapidly drive chuck temperature up
to the hot setpoint-value.
In many of the lift and pulley mechanisms illustrated, the center
through-hole of a wheel is threaded to mate with a jackscrew that
passes through it and is fixedly attached to the chiller heat
exchanger. Each wheel is captured between the base plate (e.g.,
324) and a support bracket (e.g. 318). When the wheel is turned,
the jackscrew and the attached chiller heat-exchanger move up and
down. Three sets of jackscrews and wheels are normally used to
define and retain chiller heat-exchanger and spreader surfaces in
parallel planes. The threaded jackscrew drive wheels are
simultaneously driven by a common belt or chain and motor, e.g., as
can be partially seen in FIG. 4.
Although the present invention has been described in terms of the
presently preferred embodiments, it is to be understood that the
disclosure is not to be interpreted as limiting. Various
alterations and modifications will no doubt become apparent to
those skilled in the art after having read the above disclosure.
Accordingly, it is intended that the appended claims be interpreted
as covering all alterations and modifications as fall within the
"true" spirit and scope of the invention.
* * * * *